CORVALLIS, Ore. — Organic blueberry growers can go toe to toe with commercial growers if they plant in raised beds, use a weed mat mulch and apply low amounts of nitrogen, according to a 10-year study from Oregon State University.
Bernadine Strik, OSU Extension berry crops specialist and professor in the Department of Horticulture, said that the research shows organic growers can get a higher yield at the lowest cost by using these recommendations — a pivotal finding for the organic industry, which grew from 2% of regional blueberry production in 2006 to as much as 20% in 2016.
The Pacific Northwest is now the largest organic production region for blueberries in the world.
Because organic fertilizers cost 10 times more and approved herbicides are less effective and more costly than those for conventional production, finding ways to reduce costs while increasing production is critical for organic growers.
“If you want higher financial returns, you’ve got to get higher yields,” said Strik, who led the study. “By using the key outcomes of our research, organic growers can get a similar yield to what a conventional grower gets. You can do very well using organic practices.”
First certified organic blueberry study
The first long-term, certified organic study of its kind was funded by the Oregon Blueberry Commission and the U.S. Department of Agriculture National Institute of Food and Agriculture and was published in HortScience.
To put themselves on the same playing field as their constituents, Strik and her team got their field certified organic by Oregon Tilth. Because of that effort, OSU now has the only certified organic blueberry research plot in the world.
The three-pronged study looked at the outcome of growing highbush blueberries in raised beds versus flat ground, the most efficient type and amount of fertilizer to apply, and how best to combat weeds with various mulches.
On a 1-acre field at the North Willamette Research and Extension Center in Aurora, scientists planted industry standards ‘Duke’ and ‘Liberty’ in fall 2006. Some were planted in raised beds, some on level ground. Although ‘Duke’ showed no difference in either situation, ‘Liberty’ performed better in raised beds, producing 22% better cumulative yields over the nine years of harvest.
“That’s huge,” Strik said.
To document the results, researchers took photos underground by threading plexiglass tubes fitted with cameras through the soil in the raised and flat-ground plantings.
“We were able to show significantly more root growth in the raised beds,” she said. “We suspect that’s because there’s more oxygen available.”
Because of the results of Strik’s work, a majority of growers — organic and conventional — now establish fields on raised beds.
Weed mat improves weed control and yield
The study also looked at the effects of mulch on weed control, which hits hard on the bottom line of organic growers who must pay for hand pulling or use expensive, often less effective organic herbicides. Strik and her team experimented with porous black plastic weed mat, yard debris compost topped with sawdust and sawdust on its own and hand-pulled weeds in all when needed. The weed mat proved the most effective mulch for controlling weeds, allowing for a 6% increase in cumulative yield.
“The slight increase in yield coupled with reduced weed management costs — that’s a pretty significant amount of money,” she said.
When the study started, sawdust mulch in the row was the industry standard for weed control. Fewer than 20% of new fields were established with weed mat. As the research progressed and word spread, more growers switched; now more than 80% are using it.
Fertilizer source affects cost and crop response
To find the most effective source of nitrogen fertilizer, Strik’s team compared different amounts of commonly used feather meal and fish solubles. Feather meal, applied as granules, contained 11% to 13% nitrogen, while fish emulsion, delivered by fertigation, had 3.5%. Both products were applied at equivalent “low” or “high” nitrogen rates.
“Being able to reduce the amount of fertilizers applied by half while having similar or greater yield is a huge cost savings to organic growers,” she said.
Yield was also 10% greater with feather meal than with fish solubles. ‘Duke’ was particularly sensitive to fertilizer source and produced 35% less yield overall with fish solubles than with feather meal. By contrast, there was relatively little effect of fertilizer source or rate on yield in ‘Liberty’. Many organic growers have tried reducing the rate of fish solubles applied to their ‘Duke’ fields to the lower rates studied here, with very positive results.
Key takeaways for organic success
The bottom line for growers to maximize yields and reduce costs, Strik said, is to plant on raised beds, mulch with weed mat and adjust the fertilizer source based on the cultivar grown. The key is to avoid high rates of fish solubles in the crop.
Previously titled Organic blueberry growers can compete successfully with commercial operations
